This invention relates to a ventilation device for an electronic enclosure and more particularly, to a noise-attenuating ventilation pedestal for an electronic enclosure which is adapted for use as a simple adjunct to floor-standing enclosure designs.
The reliability of all electronic devices is influenced by their operating temperatures. If the electronic device is operated below a certain temperature, it will not function properly. If the electronic device is operated above a certain temperature, it will fail permanently. The temperature at which such failure occurs decreases with time as the device is aged by operational stresses. If the device can be operated below all critical temperatures, voltages and currents, then it should be able to operate indefinitely. The higher the device is operated above these critical levels, the sooner the device will fail.
Several methodologies have been employed to reduce the operational temperatures of electronic devices. Such devices may be designed to reduce the amount of heat generated in the performance of a particular task. The device may incorporate heat sinks to enhance the ability of the device to dissipate heat. A number of devices may be arranged in a manner in which the generated heat establishes natural convection currents which may be employed to draw in cool air at the base of the enclosure and to exhaust warmer air above. The device may be placed in an actively ventilated enclosure wherein an air moving device is employed to either pump ambient air into or draw heated air out of the enclosure. The device may be actively cooled by refrigeration equipment to reduce the operational temperature below the otherwise available ambient temperature. These methods can be and are employed in various combinations.
Another source of reliability problems with electronic devices is that of contamination by foreign materials or objects. Dust, typically, accumulates near any edge or other flow stagnation points. These particulates can seriously impair the function and life of removable storage media and their interfacing devices. The dust accumulation also reduces the effective air flow near the electronic device, thus impairing its capacity for heat dissipation and thus its reliability. Increased ventilation of an electronic device can lead to increased dust accumulation upon its surfaces. One means of reducing such dust accumulation is by air filtration. Unfortunately, most manufacturers employ suction wholly or partially to move air through their enclosures. Filtration of the input air is difficult, if not impossible, under such a scheme as particulate laden air is drawn in through any and all penetrations of the enclosure.
A common design problem encountered in the design of filtered ventilation for an electronic device is that of access to the filtration media, since particulates accumulate in the media as the enclosure is ventilated. Eventually, due to clogging of the filtration media, the pressure drop across the media becomes so great that the flow through the air moving device becomes ineffective. Further, an air mover generates its own heat, thus creating a situation where the electronics are subjected to higher thermal stress with ventilation than without. The enclosure designer must therefore make the filtration system readily accessible for servicing or replacement.
In industrial environments, electronic device failure can be very costly due to line stoppage. Reliability of the electronic device is of prime importance. The noise generated by increased ventilation is minimal with respect to that generated by common industrial operations. Thus, industrial electronic devices are often highly ventilated with filtered air.
In office environments, thermal stresses and airborne particulates are not as prevalent as in industrial environments. However, noise reduction is a major concern. A noisy device will not be purchased if there is a quieter alternative available. Competition motivates manufacturers to provide quiet devices wherein the minimal amount of ventilation required for the typical environment is employed. Unfortunately, office environments vary widely. Device reliability can range from a few months to a few years under such conditions with marginal ventilation. Although technically obsolete, a device can have a useful life, from the customer's viewpoint, of many years. Increased ventilation can easily extend the reliable lifetime of a device beyond the time at which the device is replaced by new technology. A device that operates reliably throughout its useful life should be very desirable.
The means conventionally used to reduce the noise generated by ventilation involve the reduction of ventilation capacity. Low speed fans generate less noise but inherently less flow. Fans are placed internally to isolate the noise. With such placement, there is likely to be an internal recirculation component reducing the effective fresh air exchange. Exhaust ports are placed at the rear of the enclosure to limit forward propagation of noise. Little attention is paid to the noise generation characteristics of the air mover. Air movers are standardized components. The manufacturers of these air movers have made some progress in terms of airfoil design and turbulence minimization to reduce the generated noise. However, electronic device manufacturers simply add these air movers to their devices without modification. The interface between the air movers and their surroundings has been largely ignored.
Due to established standards, an electronic system can be built by simply assembling a collection of minimally compatible components. Standards describe primarily logical, electrical and physical interconnection. They rarely address thermal and electromagnetic compatibility. Inadequate attention to reliability issues is common. Reliability can be enhanced by utilization of power supplies and cooling apparatus of capacities well above minimal requirements. In the office environment, reliability through increased ventilation is compromised by the desire to minimize the resultant noise levels.